The cooling system in clouds cannot protect us from rising temperatures as expected

Global climate models may have “significantly underestimated” the increment of Earth temperatures due to greenhouse gas emissions. The error could lay on the calculus of the cooling system in clouds, according to a new report published April 9 in the journal Science.

Researchers have emphasized on mixed-phase clouds, which contain ice crystals and very cold water droplets. However, the ratio of these formations may have been “misjudged” by global climate projections, leading to a “significant under-reporting” of climate sensitivity levels, according to a Yale statement.

Researchers have emphasized on mixed-phase clouds, which contain ice crystals and very cold water droplets. Photo credit: Cloud Maven

Equilibrium climate sensitivity is a measure used to calculate the response of Earth’s surface temperatures, depending on atmospheric carbon dioxide (CO2) levels. Expressly, scientists are able to estimate Earth’s temperatures if CO2 levels duplicate its pre-industrial levels.

In 2013, the Intergovernmental Panel on Climate Change (IPCC) estimated climate sensitivity between 2 to 4.8 degrees Celsius. On the other hand, Yale researchers have obtained higher numbers, with an estimate of 5 to 5.3 degrees Celsius.

Which is the impact of higher levels of climate sensitivity?

If results are accurate, a temperature increase of that magnitude could have “dramatic implications” for Earth’s ecosystems and climate change.

“It goes to everything from sea level rise to more frequent and extreme droughts and floods. The overestimate of ice in mixed-phase clouds relative to the observations is something that many climate modelers are starting to realize.” said Ivy Tan, a Yale graduate student and lead author of the study.

Co-author Trude Storelvmo, assistant professor of geology and geophysics, explained that the new investigation has considered the composition of mixed-clouds, formed by water vapor, liquid droplets and ice particles.

It appears that a higher concentration of ice in those clouds can lead to a lower climate sensitivity, considered as a “negative climate feedback mechanism”. In other words, when ice levels in the upper atmosphere are higher, there will be less warming on the Earth’s surface.

Where is the error in previous estimates?

Storelvmo said that global climate models have “started with far too much ice”. However, results definitely changed, when the Yale team conducted its own simulations, taking mixed-phase clouds and satellite information into account. In the end, estimates showed higher temperatures.

It appears that climate feedback mechanisms of clouds were previously unknown by the scientific community. That could explain why earlier models were not so accurate. A laboratory, lead by Storelvmo at Yale, has been investigating such a phenomenon over the last years.

The Intergovernmental Panel on Climate Change will issue a new updated report in 2020. Researchers mentioned that correcting the ice-water ratio in global models is fundamental. This research have been supported by the NASA and Space Science Fellowship Program, the National Science Foundation and the U.S. Department of Energy.